270 ANIMAL PHYSIOLOGY. 



other membrane to the end of a tube, and holding it so as 

 to leave a chink between two tight edges. As long as the 

 edges are inclined one to the other, or are parallel, a note is 

 produced by blowing through the tube; but when the edges 

 are everted, the sound ceases. 



Fig. 136. LARYNX, from above; laryngoscopic views: A, in deep 

 respiration, showing the trachea down to its bifurcation ; B, in 

 uttering a high pitched note, a, Epiglottis; &, c, swellings cor- 

 responding to cartilaginous nodules of Wrisberg and Saiitorini; 

 d, true vocal cord; e, false vocal cord. After Czermak. 



The note produced by vibrating strings and laminae is 

 dependent on two things, namely, the length of the string or 

 free edge, and the degree of tension. Both these principles 

 are illustrated in the human larynx. The reason why the 

 voices of women and children are higher in pitch than those 

 of adult men is, that in women and children the larynx is 

 smaller and the vocal cords are shorter; and in boys, at the 

 age when the voice begins to grow rough, an obvious enlarge- 

 ment of the larynx, as judged by the prominence of the 

 pomum Adami, may be observed. But the different notes 

 of any one voice are produced by varying tension of the 

 vocal cords. This may be easily proved by placing a finger 

 over the space occupied by the crico-thyroid membrane and 

 running over the gamut, when the thyroid cartilage will be 

 felt gradually coming down over the cricoid, in the manner 

 which has been already shown to stretch the vocal cords. 

 At the same time, the whole larynx rises more nearly to a 

 level with the tongue, and hence the comparative clearness 

 of the higher notes. 



The various cavities above the level of the vocal cords, 

 acting as resonating chambers, determine the timbre of the 



